class Solution {
public:
    int maxProfit(vector<int>& prices) {
      int len = prices.size();
      vector<vector<int> > dp(len,vector<int>(2,0));
      dp[0][0] = 0;
      dp[0][1] = -prices[0];
      for(int i = 1;i < len;i++){
        dp[i][0] = max(dp[i-1][0],dp[i-1][1] + prices[i]);
        dp[i][1] = max(dp[i-1][1],-prices[i]);
      }
      return dp[len-1][0];
    }
};
